| In today’s society,with the continuous progress of science and technology,automobile manufacturing technology is developing rapidly,but with the sharp increase in the number of traditional fuel vehicles,the gradual shortage of traditional energy and the deterioration of human living environment,pure electric vehicles are rising rapidly.Distributed drive electric vehicle belongs to pure electric vehicle,the braking system of this kind of vehicle not only uses traditional hydraulic brake,but also combines motor brake and hydraulic brake,which can improve the performance of vehicle braking process.It can also recover energy and improve the driving range of the vehicle.The focus of the research on the compound braking system of distributed drive electric vehicles lies in the reasonable distribution of braking force and the effective and feasible control strategy,which fully guarantees the good stability of the vehicle during braking,and recovers as much braking energy as possible on this basis.Therefore,this paper designs a composite braking scheme under the premise of extensive analysis of domestic and foreign composite braking research,proposes a layered control strategy for distributed drive electric vehicle composite braking system,and conducts joint simulation analysis for verification.First of all,starting from the structure,the distributed drive electric vehicle is analyzed as a whole,focusing on the in-depth analysis of its compound braking system,and the compound braking scheme is designed.The dynamic performance of the vehicle is analyzed,on the basis of which the parameters of the main components are matched and selected.Secondly,based on the idea of hierarchical control,the braking force distribution strategy of compound braking system is put forward.The control goal of upper control is to ensure the braking stability in the process of vehicle braking.The sliding mode control algorithm based on reaching law is used to distribute the front and rear axle braking torque,and the conventional and anti-lock braking conditions are comprehensively considered.The goal of the lower level control is to recover as much braking energy as possible while ensuring braking safety.The regenerative braking torque provided by the motor and the braking torque provided by the hydraulic system are distributed by considering the SOC value,vehicle speed,maximum motor torque,battery charging power and braking intensity and using them as constraint factors.Finally,based on the joint simulation verification of MATLAB/Simulink software and AMESIM software,the whole vehicle model of distributed drive electric vehicle is built by AMESim software,and the control model of compound braking system is built by Matlab/Simulink software.Simulation analysis is carried out under various operating conditions,and compared with the traditional compound brake parallel control strategy.The simulation results under multiple operating conditions show that using the compound braking hierarchical control strategy designed in this paper,under the conventional braking conditions,the front and rear wheel speed is lower than the vehicle speed and there is little difference,and the braking time is in a reasonable range.Fully ensure the braking efficiency during braking.The slip rates of the three initial braking speeds are stable at 0.78%,1.7% and 3.1% respectively,and the braking stability is good.At the same time,the highest energy recovery rates under the three conventional braking conditions are 55.9%,71.8% and74.7%,respectively.Under the condition of anti-lock braking,the front and rear wheel slip rates can be maintained near the optimal slip rate,and the energy recovery rate is 72.4%.The goal of recovering as much braking energy as possible is achieved.Compared with the traditional parallel control strategy,the hierarchical control strategy designed in this paper is better than the parallel control strategy in braking efficiency and energy recovery,which proves that the control strategy designed in this paper is feasible. |
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